Isotope studies on crop utilization and soil fixation of nitrogen from calcium nitrate, ammonium sulphate and urea in several Manitoba soils

Abstract:

Crop utilization and soil fixation of nitrogen from three 15N-labelled N-carriers were studied on several Manitoba soils. In a growth chamber study, more nitrogen from Ca(NO3)2 was utilized by wheat than from (NH2)2CO in the slightly acid soils. The `A' value indicates that Ca(NO3)2 is more available to wheat than (NH2)2CO on the slightly acid soils. Dry matter yield of wheat was significantly greater with Ca(NO3)2 treatment than with (NH2)2CO in Pine Ridge, Wellwood and Granville soils. A much greater part of NH4+/-N from (NH2)2CO than NO3-/-N from Ca(NO3)2 remained in all soils at the end of the experiment. The oxidation of NH4+/-N from urea was slower in the slightly acid soils. Persistence of NH4+/-N might lead to fixation of this form of N in slightly acid soils... An incubation study showed that more of the N added as urea or ammonium sulphate was fixed than of the N added as Ca(NO3)2 in all soils used... Most of the added N fixed in the soils was organically bound... Liming Pine Ridge and Wellwood soils decreased the amount of added N fixed from NH4+/-yielding carriers, but did not significantly increase the dry matter yield of wheat on these soils. Utilization of added N by wheat from NH4+/-yielding carriers was brought closer to that of Ca(NO3)2 when Pine Ridge and Wellwood soils were limed. In acidified Newdale soil, more N from Ca(NO3)2 was utilized by wheat than N from NH4+/-yielding carriers. Acidifying Newdale soil increased the added N fixed and consequently decreased the utilization of N from both ammonium carriers.